Son of a Gun, origin and meaning.

Although there are a number of interpretations, there appears to be consensus that this expression is of nautical origin.
The expression is usually used in a derogatory manner when the parentage if a person is questioned. “Son of a Bitch” most probably evolved from this saying, and is more commonly used today.
Originated during the days of sailing ships.
It would appear as though sailors were permitted female company either during voyages or while in ports. A child conceived where the father was “unknown” or where the father was not named, was called “ a son of a gun”. Conception would most probably have take place on one of the gun decks next to the guns, as this would have been the only place of privacy for the sailors. (“Sons between guns”)
Son of a Gun was/is used to infer illegitimacy and convey contempt.
Another version is that women were allowed to enlist in non-combative roles in days past, and would give birth at sea on the gun deck between the guns.
Associated to this version was the firing of cannon next to the expectant mother during a difficult labour, to hasten the process. I was present at the birth of my 3 children, and firing a cannon right next to me during this process would have caused WW III.
My father was English, from a military family and a World War II veteran. He often used the expression “son of a gun”, with admiration. Up until today, I personally never knew that the expression was derogatory. This gives credence to the other possible origin, namely that a “son of a gun” was the son of a Soldier or a bearer of arms.
Post suggested by JonnyStensby, Norwegian expat in South Africa